mid-14c., " act, crime, or sin of killing another human being," in battle or not, from man (n.) + slaughter (n.). Replaced Old English mannslæht (Anglian), mannslieht (West Saxon), from slæht, slieht "act of killing" (see slay). Etymologically identical with homicide, but in legal use usually distinguished from murder and restricted to "simple homicide."

The unlawful killing of a person, without malice or premeditation. Involuntary manslaughter is accidental, such as running into someone with a car. Voluntary manslaughter is committed in the “heat of passion,” as in a spontaneous fight in which one person is killed by a strong blow. Manslaughter is usually considered less serious than murder. Both murder and manslaughter are types of homicide.